Proton exchange membrane fuel cell stack and fuel cell stack module

ABSTRACT

A proton exchange membrane fuel cell stack and novel proton exchange membrane fuel cell module are disclosed and wherein the proton exchange membrane fuel cell stack includes a plurality of repeating, serially electrically coupled fuel cell stack modules, and which are sealably mounted together by a compressive force of less than about 60 pounds per square inch.

PRIORITY

This utility application is a continuation of, and claims priority from,U.S. application Ser. No. 11/800,994, filed on 2007-05-08.

TECHNICAL FIELD

The present invention relates to a proton exchange membrane fuel cellstack and a fuel cell stack module, and more specifically, to a protonexchange membrane fuel cell stack comprised of a plurality of serially,electrically connected fuel cell stack modules, which are coupledtogether by a reduced compressive force, and which achieves optimalelectrical performance at a pressure less than the reduced compressiveforce.

BACKGROUND OF THE INVENTION

A fuel cell is an electrochemical device which reacts hydrogen, a fuelsource, and oxygen, which is usually derived from the ambient air, toproduce electricity, water, and heat. The basic process is highlyefficient, and fuel cells fueled by pure hydrogen are substantiallypollution free. Further, since fuel cells can be assembled into modulesof various sizes, power systems have been developed to produce a widerange of electrical power outputs. As a result of these attributes, fuelcell power systems hold a great deal of promise as an environmentallyfriendly and viable source of electricity for a great number ofapplications.

One of a number of known fuel cell technologies is the proton exchangemembrane (PEM) fuel cell. The fundamental electrochemical process underwhich PEM fuel cells operate is well understood and known in the art. Atypical single PEM fuel cell produces a useful voltage of about 0.45 toabout 0.70 Volts DC, although most fuel cells are operated at about 0.60Volts DC in order to extract the greatest efficiency from same. Toachieve a useful voltage, typically a number of individual fuel cellsare electrically combined or coupled in series. In one commonconfiguration, a number of individual fuel cells are electricallycoupled in series in the form of a fuel cell stack. In a stackconfiguration, the anode of one fuel cell is electrically coupled to thecathode of another fuel cell in order to connect the two fuel cells inseries. Any number of fuel cells can be similarly stacked together toachieve the desired output voltage and current. Typically, theseindividual fuel cells are separated by an electrically conductivebipolar separator plate. Further, the individual fuel cells are placedbetween two end plates and a substantial compressive force is applied tosame in order to effectively seal same, and to achieve an operativelyeffective ohmic electrical connection between the respective fuel cells.

In addition to the relatively low operating temperature PEM fuel cellsnoted, above Solid Oxide Fuel Cells (SOFC) have been developed. A SOFCis a fuel cell which generates electricity directly from a chemicalreaction, yet unlike PEM fuel cells, an SOFC is typically composed ofsolid ceramic materials. The selection of the materials employed in suchprior art SOFC devices is dictated, to a large degree, by the highoperating temperatures (600-800 degrees C.) which are experienced bysuch devices. In view of the extremely high operating temperatures whichare needed to render the ceramic based electrolyte ionically active,SOFC devices do not require the use of an expensive catalyst (platinum),which is the case with PEM fuel cells as discussed, above. As a resultof these high operating temperatures, assorted fuels can be employedwith a SOFC which could not normally be used in a PEM fuel cell.Therefore, SOFC devices can employ fuels such as methane, propane,butane, fermentation gas, gasified biomass, etc. In a typical SOFCdevice, a ceramic based electrolyte formed of a material such aszirconium oxide is sandwiched between a porous, electrically conductivecathode layer, and a porous, electrically conductive anode layer. Thesecathode and anode layers are typically ceramic gas diffusion layers thatare selected for their structural rigidity and high temperaturetolerance. The chosen electrolyte must be impervious to air (oxygen) andmust be electrically insulating so that the electrons resulting from theoxidation reaction on the anode side are forced to travel through anexternal circuit before reaching the cathode side of the SOFC. In atypical SOFC device a metal or electrically conductive interconnectelectrically couples the respective cells in a serial arrangement. If aceramic interconnect is employed it must be extremely stable because itis exposed to both the oxidizing and reducing side of the SOFC at hightemperatures.

As should be understood from the discussion above, the cost offabricating such SOFC devices is significant. Further, to render suchdevices operational, a rather significant and sophisticated balance ofplant arrangement must be employed to controllably heat the SOFC deviceup to an operational temperature, and then maintain the device within anacceptable temperature range. In contrast, PEM fuel cells do not needthe extremely high temperatures employed in SOFC devices in order torender the electrolyte (typically Nafion) ionically active. Furtherthese high temperatures have dictated the use of heat tolerant ceramicmaterials for the anode and cathode. The cost of fabricating thesecomponents is significant. In typical PEM fuel cell devices, thedesigners of same have continually strived to employ lower costcomponents, and simplify any balance of plant requirements in order toreduce the cost of same and make the cost per watt of power generatedmore acceptable for discreet market applications.

While traditional PEM fuel cell stacks have operated with some degree ofsuccess, a number of shortcomings continue to distract from theirusefulness. First among these shortcomings is the high cost ofmanufacture for the individual components of a traditional stack design.Chief among these high cost components is the bipolar plate which isemployed with same. In order to save costs, many manufacturers of fuelcell stacks have attempted to combine a number of functions into thebipolar plate. A modern bipolar plate is a precisely fabricatedcomponent that performs a number of functions including fuel management,cooling, electrical conduction, and gas separation. The result of thiscombination of functions is that performance in many areas must besacrificed in order to save costs. Examples of such an arrangement areseen in U.S. Pat. Nos. 5,252,410, and 5,863,671, the teachings of whichare incorporated by reference herein.

Another primary cost or factor which impacts a traditional fuel cellstack is that attributed to the force compression needed to make suchdevices operational. In order to achieve an operationally effectiveelectrical conductivity between a proton exchange membrane, a gasdiffusion layer, and/or a bipolar plate, a great deal of force must beapplied between the end plates of the traditional stack. Typically,these compression forces are in excess of 100 pounds per square inch. Toachieve this level of compressive force, costly, heavy, and complexcomponents are often required. The application of this force typicallycompresses same components within a stack, for those components whichare porous, this same force may reduce the porosity of same. Yet anothershortcoming attributable to the traditional fuel cell stack design orarrangement is heat management. Because a fuel cell generates heat whilegenerating electricity, excess heat is often created and accumulates inthe center and other locations within the stack. A number ofsophisticated technologies and designs have been developed to managethese hotspots, but the result has been higher manufacturing costs andgreater complexity for a resulting fuel cell stack system.

One proposed solution to the problems associated with the cost andcomplexity of prior art force compression arrangements was disclosed inU.S. Pat. No. 6,716,549, the teachings of which are hereby incorporatedby reference. This proposed solution involved coating a surface of atraditional, rigid, carbon gas diffusion layer with a metal such thatthe resulting metalized gas diffusion layer retained its porosity. Theresulting metalized surface of the carbon gas diffusion layer forms anohmic contact with an adjacent metal current collector without the needfor the high compression forces that would typically be required withoutthe metal layer. While this solution addresses some of the issuesassociated with force compression, it still requires the use of a rigidcarbon, gas diffusion layer, which has become increasingly costly anddifficult to procure. Thus, a long felt need remains for a lower cost,and higher performing alternative to the prior art high forcecompression proton exchange membrane fuel cell stacks which are nowdisclosed in the art.

The prior art is replete with numerous examples of other prior art fuelcell devices that attempt to address these and other issues. TheOffice's attention is directed to U.S. Pat. Nos. 5,470,671; 5,482,792;and U.S. Application Publication No. 2006/0134498; the teachings ofwhich are incorporated by reference herein.

A proton exchange membrane fuel cell stack and an associated protonexchange membrane fuel cell stack module which avoids the shortcomingsattendant with the prior art devices and practices utilized heretoforeis the subject matter of the present application.

SUMMARY OF THE INVENTION

A first aspect of the present invention relates to a proton exchangemembrane fuel cell stack which includes a plurality of repeating,serially electrically coupled fuel cell stack modules, which aresealably mounted together by a compressive force of less than about 60pounds per square inch.

Another aspect of the present invention relates to a proton exchangemembrane fuel cell stack which includes first and second endplatesdisposed in substantially parallel spaced relation; and a plurality ofrepeating, air-cooled, fuel cell stack modules positioned between thefirst and second endplates, and which are serially electrically coupledtogether, and wherein the respective endplates sealably couple therespective fuel cell stack modules together by applying a compressiveforce of less than about 60 pounds per square inch to each of therespective fuel cell stack modules, and wherein the proton exchangemembrane fuel cell stack has an operational temperature profile asmeasured between the first and second end plates which varies by lessthan about 10%.

Still another aspect of the present invention relates to a protonexchange membrane fuel cell stack module which includes a protonexchange membrane having an anode side, and a cathode side; a first gasdiffusion layer juxtaposed relative to the anode side; a second gasdiffusion layer juxtaposed relative to the cathode side; an electricallyconductive heat sink having a thermally conductive mass juxtaposedrelative to the second gas diffusion layer; and a current collectingseparator plate juxtaposed in ohmic electrical contact relative to thefirst gas diffusion layer, and wherein a plurality of fuel cell stackmodules are electrically connected in series, and are further mountedbetween a first and second endplate to form a fuel cell stack, andwherein the current collecting separator plate of a first fuel cellmodule is juxtaposed relative to the first endplate, and wherein theheat sink of a remote, second fuel cell module is positioned in forcereceiving relation relative to the second endplate, and wherein thefirst and second endplates provide a compressive force of less thanabout 60 pounds per square inch to each of the plurality of protonexchange membrane fuel cell stack modules.

Yet another aspect of the present invention relates to a proton exchangemembrane fuel cell stack which includes a plurality of repeating,serially electrically coupled fuel cell stack modules, which aresealably mounted together by a compressive force of less than about 60pounds per square inch, and wherein the respective fuel cell stackmodules further comprise a frame having an inside and an outsideperipheral edge, and first and second sides, and wherein the insideperipheral edge defines an internal cavity, and wherein the respectiveframes are self-aligning and matingly nest together in an operationalorientation, and wherein the respective frames each define an airpassageway which extends between the inside and outside peripheral edgesand which communicates with the internal cavity thereof.

Further, another aspect of the present invention relates to a protonexchange membrane fuel cell stack module which includes a protonexchange membrane having an anode side, and a cathode side; a first gasdiffusion layer juxtaposed relative to the anode side; a second gasdiffusion layer juxtaposed relative to the cathode side; an electricallyconductive heat sink juxtaposed relative to the second gas diffusionlayer; a frame having an inside and an outside peripheral edge, andfirst and second sides, and wherein the inside peripheral edge definesan internal cavity therewithin the frame, and wherein the protonexchange membrane, the first and second gas diffusion layers, and theheat sink are enclosed within the internal cavity; and a first currentcollecting separator plate mounted on the first side of the frame, andjuxtaposed relative to the first gas diffusion layer, so as to form afuel cell stack module, and wherein a plurality of fuel cell stackmodules are positioned between a first and a second endplate, and arefurther serially electrically coupled together, and wherein therespective endplates apply a compressive force of less than about 60pounds per square inch on each of the respective fuel cell stackmodules.

Another aspect of the present invention relates to a proton exchangemembrane fuel cell stack which includes a plurality of repeatingserially electrically coupled fuel cell stack modules, each defining aninternal cavity and which are sealably mounted together by a compressiveforce of less than about 60 pounds per square inch; and a protonexchange membrane is placed in a operational orientation relative to atleast one ceramic gas diffusion layer and which is received within thecavity of the respective fuel cell stack modules.

Still another aspect of the present invention relates to a protonexchange membrane fuel cell stack which includes first and secondendplates disposed in substantially parallel spaced relation; and aplurality of repeating, air-cooled, fuel cell stack modules positionedbetween the first and second endplates, and which are seriallyelectrically coupled together, and which further has an operationallyeffective conductivity, as measured between the first and secondendplates, which is achieved at a pressure less than a compressive forceapplied to each of the plurality of the fuel cell stack modules, andwhich further has an operationally effective temperature profile asmeasured between the first and second end plates which is substantiallyuniform.

Yet another aspect of the present invention relates to a proton exchangemembrane fuel cell stack module which includes a proton exchangemembrane having an anode side and a cathode side; a first electricallyconductive ceramic layer juxtaposed relative to the anode side; a secondelectrically conductive ceramic layer juxtaposed relative to the cathodeside; an electrically conductive heat sink juxtaposed relative to thesecond electrically conductive ceramic layer; a frame having an insideand an outside peripheral edge, and first and second sides, and whereinthe inside peripheral edge defines an internal cavity, and wherein therespective frames each define an air passageway which extends betweenthe inside and outside peripheral edges and which communicates withinternal cavity thereof, and wherein the proton exchange membrane, firstand second electrically conductive ceramic layers, and the electricallyconductive heat sink are enclosed within the internal cavity; and acurrent collecting separator plate mounted on the first side of theframe, and which is juxtaposed relative to the first electricallyconductive ceramic layer.

Another aspect of the present invention relates to a proton exchangemembrane fuel cell stack which includes a first endplate and an oppositesecond endplate; a plurality of fuel cell stack modules mounted betweeneach of the first and second endplates, and wherein each of the fuelcell stack modules further include a proton exchange membrane having ananode side and a cathode side; a first electrically conductive ceramicdiffusion layer juxtaposed relative to the anode side; a secondelectrically conductive ceramic gas diffusion layer juxtaposed relativeto the cathode side; an electrically conductive heat sink juxtaposedrelative to the second ceramic gas diffusion layer, and wherein the heatsink defines a plurality of fluid passageways which permits a source ofair to pass therethrough and reach the second ceramic gas diffusionlayer; a frame having first and second sides and an inside and anoutside peripheral edge, and wherein the inside peripheral edge definesan internal cavity, and wherein the proton exchange membrane, the firstand second ceramic gas diffusion layers, and the heat sink are enclosedwithin the internal cavity, and wherein the frame defines a fuel andexhaust gas passageway, which are each disposed in fluid flowingrelation relative to the first ceramic gas diffusion layer, and whereinthe frame further defines an air passageway, which is oriented in fluidflowing relation relative to the heat sink, and wherein the framefurther has a mounting flange which extends into the internal cavity,and substantially circumscribes the inside peripheral edge of the frame,and wherein the proton exchange membrane is sealably affixed to themounting flange; a first current collecting separator plate mounted onthe first side of the frame, and juxtaposed relative to the first gasdiffusion layer; and a second current collecting separator platejuxtaposed relative to the second endplate, and wherein the firstcurrent collecting separator plate of a first fuel cell module isjuxtaposed relative to the first endplate, and wherein the secondcurrent collecting separator plate is juxtaposed relative to the heatsink of a second fuel cell module, which is located adjacent to thesecond endplate, and wherein the first and second endplates provide acompressive force to each of the plurality of fuel cell modules which isless than about 60 pounds per square inch.

Another aspect of the present invention relates to a proton exchangemembrane fuel cell stack which includes a plurality of frames, eachhaving an inside and an outside peripheral edge, and first and secondsides, and wherein the inside peripheral edge defines an internalcavity, and wherein the respective frames are self-aligning and matinglynest together in an operational orientation, and wherein the respectiveframes each define an air passageway which extends between the insideand outside peripheral edges and which communicates with the internalcavity thereof, and wherein each of the respective frames furtherdefines a fuel gas passageway which is coupled in fluid flowing relationrelative to a plurality of fuel gas channels, and which are defined, atleast in part, by the first side of each of the frames, and wherein eachof the fuel gas channels are coupled in fluid flowing relation to theinternal cavity of the frame, and wherein the individual fuel gaspassageways of the respective fuel cell stack modules are each coupledin fluid flowing relation, one relative to the others, and wherein theframe further defines an exhaust gas passageway which is coupled influid flowing relation relative to a plurality of exhaust gas channels,and which are defined, at least in part, by the first side of the frame,and wherein the individual exhaust gas channels are coupled in fluidflowing relation to the internal cavity of the frame, and wherein theindividual exhaust gas passageways of the respective fuel cell stackmodules are each coupled in fluid flowing relation, one relative to theothers; a mounting flange made integral with the inside peripheral edgeof each of the frames, and which is disposed in a substantially coplanarorientation relative to the first side of each of the frames, andwherein the mounting flange extends into the internal cavity of each ofthe frames and defines an aperture which communicates with the internalcavity of the frames, and wherein the mounting flange has first andsecond sides, and a thickness dimension defined by the distance betweenthe first and second sides; a first gas diffusion layer having an insideand an outside facing surface, and which is positioned within theinternal cavity of the frame, and wherein the outside facing surface ofthe first gas diffusion layer is oriented in a substantially coplanarorientation relative to the first side of the frame, and has a thicknessdimension substantially similar to the thickness dimension of themounting flange, and wherein the first gas diffusion layer substantiallyoccludes the aperture defined by the mounting flange; a proton exchangemembrane received within the internal cavity of the frame, and disposedin resting, sealing relation relative to the mounting flange, andwherein the proton exchange membrane has an anode side which isjuxtaposed relative to the inside facing surface of the first gasdiffusion layer, and an opposite cathode side; a second gas diffusionlayer which is positioned within the internal cavity of the frame andwhich is juxtaposed relative to the cathode side of the proton exchangemembrane; an electrically conductive heat sink having an inside and anoutside facing surface, and which is received within the internal cavityof each of the frames, and wherein the inside facing surface thereof isjuxtaposed relative to the second gas diffusion layer, and wherein theoutside facing surface of the heat sink is oriented in a substantiallycoplanar orientation relative to the second side of each of the frames,and is further oriented in fluid flowing relation relative to the airpassageway which is defined by the frame, and wherein the heat sink hasa thickness dimension which is greater than about 10 millimeters; acurrent collecting separator plate mounted on the first side of each ofthe frames, and which is further positioned, at least in part, in ohmicelectrical contact with the first gas diffusion layer, and wherein theelectrically conductive heat sink is disposed in ohmic electricalcontact with the current collecting separator plate of an adjacent fuelcell stack module, and wherein the current collecting separator platematingly couples with, and is self-aligning relative to, the frame, andwherein the current collecting separator plate is further a non-porous,substantially smooth metal plate which is bonded to the first side ofthe frame so as to effectively seal the plurality of fuel gas, andexhaust gas channels which are defined by the first side of the frame;and a first and a second endplate which are disposed in predeterminedspaced relation, one relative to the other, and wherein the plurality offrames are located between, and are disposed in force receiving relationrelative to, the first and second endplates, and wherein the respectivefirst and second endplates exert a compressive force of less than about60 pounds per square inch to each of the respective frames.

Yet another aspect of the present invention relates to a proton exchangemembrane fuel cell stack which includes a plurality of proton exchangemembranes each having an anode side, and a cathode side; a first porous,electrically conductive ceramic layer juxtaposed relative to the anodeside of each of the proton exchange membranes; and a second porous,electrically conductive ceramic layer juxtaposed relative to the cathodeside of each of the proton exchange membranes, and wherein the protonexchange membrane fuel cell stack has an operational temperature whichis less than about 200 degrees C.

Still another aspect of the present invention relates to a protonexchange membrane fuel cell stack which includes a plurality ofrepeating, serially electrically coupled fuel cell stack modules, whichare sealably mounted together by a compressive force of less than about60 pounds per square inch, and wherein the respective fuel cell stackmodules further comprise a frame having an inside and an outsideperipheral edge, and wherein the inside peripheral edge defines aninternal cavity, and wherein the respective frames each define an airpassageway having a cross sectional area, and which extends between theinside and outside peripheral edges, and which further communicates withthe internal cavity thereof, and wherein a proton exchange membranehaving an effective operating temperature is received within theinternal cavity of each of the frames, and wherein an electricallyconductive heat sink having a thermally conductive mass is receivedwithin the internal cavity of the respective frames, and which isfurther oriented in fluid flowing relation relative to the airpassageway which is defined by the frame, and which dissipates heatenergy generated by the proton exchange membrane, during operation, andwherein the operating temperatures of the respective proton exchangemembranes of the proton exchange membrane fuel cell stack are withinless than about ten percent of each other.

Yet another aspect of the present invention relates to a proton exchangemembrane fuel cell stack module which includes a proton exchangemembrane having an anode side, and a cathode side, and wherein the anodeand cathode sides each have an active area surface, and wherein theactive area surface of at least one of the anode side or the cathodeside of the proton exchange membrane, and/or a fuel cell componenthaving a region which is oriented at least in partial covering relationrelative thereto, is substantially devoid of predetermined passagewaysfor accommodating the flow of a reactant gas.

Still another aspect of the present invention relates to a protonexchange membrane fuel cell stack which includes a plurality of protonexchange membranes, each having an anode side, and a cathode side, andwherein each of the anode and cathode sides have an active area surface,and wherein the active area surface of the anode side of the protonexchange membrane, and a fuel cell stack component having a region in atleast partial covering relation relative to the active area surface ofthe anode side, are both substantially devoid of predeterminedpassageways for accommodating the flow of a reactant gas; a plurality offirst gas diffusion layers juxtaposed relative to each of the anodesides, respectively; a plurality of second gas diffusion layersjuxtaposed relative to each of the cathodes side, respectively; and aplurality of current collecting separator plates juxtaposed in ohmicelectrical contact relative to each of the first gas diffusion layers,respectively.

These and other aspects of the present invention will be described ingreater detail hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a schematic representation of a fuel cell power system whichemploys features of the present invention.

FIG. 2 is a perspective view of one form of a proton exchange membranefuel cell stack of the present invention.

FIG. 3 is an exploded, perspective view of the form of the protonexchange membrane fuel cell stack as seen in FIG. 2.

FIG. 4 is an exploded perspective view of another form of a protonexchange membrane fuel cell stack of the present invention.

FIG. 5 is a fragmentary, exploded, perspective view of one form of aproton exchange membrane fuel cell stack module, which forms a featureof the present invention.

FIG. 6 is a fragmentary, exploded, perspective view of the same protonexchange membrane fuel cell stack module taken from a position oppositeto that seen in FIG. 5, and which forms a feature of the presentinvention.

FIG. 7 is a perspective view of another form of a proton exchangemembrane fuel cell stack of the present invention.

FIG. 8 is a perspective, side elevation view of one form of a protonexchange membrane fuel cell stack module frame which forms a feature ofthe present invention.

FIG. 9 is a perspective, side elevation view of another form of a protonexchange membrane fuel cell stack module frame which forms a feature ofthe present invention.

FIG. 10 is a perspective, side elevation view of yet another form of aproton exchange membrane fuel cell stack module frame which forms afeature of the present invention.

FIG. 11 is a second perspective, side elevation view of the protonexchange membrane fuel cell stack module frame, and which is taken froma position opposite to that seen in FIG. 9.

FIG. 12 is a perspective view of yet another form of a proton exchangemembrane fuel cell stack which forms a feature of the present invention.

FIG. 13 is a top plan view of one form of a heat sink, fabricated from areticulated metal foam, and which forms a feature of the presentinvention.

FIG. 14 is a side elevation view of the same heat sink as seen in FIG.13.

FIG. 15 is a second, side elevation view of the same heat sink as seenin FIG. 13 and which is fabricated with different dimensions.

FIG. 16 is a perspective, side elevation view of a corrugated metal heatsink which forms a feature of the present invention.

FIG. 17 is a perspective, side elevation view of an extruded aluminumheat sink which forms a feature of the present invention.

FIG. 18 is a perspective, side elevation view of a stamped, resilient,reticulated heat sink which forms a feature of the present invention.

FIG. 19 is a perspective, side elevation view of a heat sink having aplurality of cooling channels, and which forms a feature of the presentinvention.

FIG. 20 is a side elevation view of the heat sink as illustrated in FIG.19, but with variably sized cooling channels which forms a feature ofthe present invention.

FIG. 21 is a perspective, side elevation view of yet another form of aproton exchange membrane fuel cell stack which forms a feature of thepresent invention.

FIG. 22 is a greatly exaggerated, exploded, transverse, verticalsectional view of a proton exchange membrane positioned between ceramicgas diffusion layers, each having a catalyst layer applied thereto.

FIG. 23 is a greatly enlarged, exploded, transverse, vertical sectionalview of a proton exchange membrane electrode assembly and which ispositioned therebetween a pair of ceramic gas diffusion layers.

FIG. 24 is a greatly enlarged, exploded, transverse, vertical sectionalview showing a proton exchange membrane electrode assembly positionedtherebetween two ceramic gas diffusion layers, and wherein one gasdiffusion layer is larger than the other.

FIG. 25 is a greatly enlarged, transverse, vertical sectional view of aproton exchange membrane electrode assembly having a gas diffusion layerwhich has a metalized coating applied thereto, and which forms a featureof the present invention.

FIG. 26 is a greatly enlarged, exploded, transverse, vertical sectionalview of the arrangement as seen in FIG. 25.

FIG. 27 is a perspective exploded, greatly enlarged, transverse,vertical sectional view of a sintered metal mesh, which is used in oneform of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Referring now to FIG. 1, a proton exchange membrane (PEM) fuel cellstack power system is generally indicated by the numeral 10 therein. Asseen in this greatly simplified view, the PEM fuel cell stack powersystem 10 includes an air-permeable housing or cabinet 11 which may bemounted on a supporting surface (not shown). The housing 11 includes aplurality of sidewalls 12, which define individual compartments, andfurther support subracks, which are generally indicated by the numeral13, and which support and otherwise enclose, at least in part, the novelproton exchange membrane fuel cell stacks which will be discussed ingreater detail hereinafter. The housing 11 may further supportindividual moveable doors 14 which allow an operator (not shown) to gainaccess to the individual compartments for repair or replacement of theindividual proton exchange membrane fuel cell stacks that will bedescribed below. Still further, the fuel cell stack power system 10includes a digital control system which is generally indicated by thenumeral 15, and which is mounted typically on the housing 11, but whichcould also be positioned remotely relative thereto. The digital controlsystem 15 which controls the operation of the fuel cell power stacksystem 10 is well known in the art. The Office's attention isspecifically directed to U.S. Pat. No. 6,387,556, the teachings of whichare incorporated by reference herein. The digital control system 15 mayinclude, among other things, an alpha-numeric display 16 which providesinformation to an operator regarding the operational features andperformance of the fuel cell stack power system 10, and further mayinclude other controls 17, such as switches, dials, and the like, whichallow an operator (not shown) to control the operation of the fuel cellstack power system 10.

The invention 10 as seen in FIG. 1 contemplates an electricalarrangement whereby a proton exchange membrane fuel cell stack, as willbe described hereinafter, may be deactivated and removed from thehousing or cabinet 11 while the remaining proton exchange membrane fuelcell stacks, as will be described, remain operational and continue toservice a load 20 as seen in FIG. 1. This performance feature is wellknown in the art and has been employed heretofore in modular fuel cellswhich are more fully described in such references as U.S. Pat. Nos.6,030,718 and 6,468,682, the teachings of which are incorporated byreference herein, and others. As seen in FIG. 1, an electrical conduit21 electrically couples the proton exchange membrane fuel cell powersystem 10 with the electrical load 20 to be serviced. The protonexchange membrane fuel cell power system 10 generates electricity bywell known means as described earlier in this application. The protonexchange membrane fuel cell stack, as will be described below, issupplied with a reactant fuel gas from a source generally indicated bythe numeral 30. The source of the reactant fuel gas 30 may also be apressurized hydrogen bottle 31 which provides pure hydrogen underpressure to the proton exchange membrane fuel cell power system 10.Still further, the source of reactant fuel gas 30 may include a hydrogengenerator, fuel processor, or reformer 32 which may provide a hydrogenrich reformate stream or substantially pure hydrogen to the protonexchange membrane fuel cell power system 10. As seen in FIG. 1, each ofthe sources of a reactant fuel gas 30 may be coupled to the fuel cellpower system 10 by means of hydrogen delivery conduits, generallyindicated by the numeral 33.

One possible form of a proton exchange membrane fuel cell stack whichforms a feature of the present invention is generally indicated by thenumeral 40 in FIG. 4. As best seen in FIG. 4, this form of the protonexchange membrane fuel cell stack 40 includes a first end plate 41 and asecond end plate 42. The first end plate 41 has a main body generallyindicated by the numeral 43. The main body includes an inside facingsurface 44, and an opposite outside facing surface 45. Still further,the main body is defined by a peripheral edge 46. As seen in FIG. 4, forexample, it should be understood that tie rod apertures 50 are formed inthe main body 43 and extend between the inside and outside facingsurfaces 44 and 45 thereof. As should be understood, tie rod aperturesare operable to receive a tie rod, as will be described hereinaftertherethrough, and which allow the first and second end plates 41 and 42,respectively, to be urged one towards the other in order to exert acompressive force on fuel cell module frames, which will be discussed ingreater detail hereinafter. In this regard, the main body 43 of thefirst end plate 41 further has formed therein a fuel gas passagewaywhich is generally indicated by the numeral 51, and a exhaust gaspassageway generally indicated by the numeral 52. The fuel and exhaustgas passageways 51 and 52 extend between the inside and outside facingsurfaces 44 and 45. The fuel gas passageway 51 allows the passage of asuitable fuel gas from a source 30 to be supplied to the proton exchangemembrane fuel cell stack 40. The exhaust gas passageway allows anexhaust gas, which may include a combination of both unused fuel gas andwater vapor, to escape in an efficient manner from the proton exchangemembrane fuel cell stack 40. As seen in FIG. 4, the second end plate 42similarly has a main body 53 which is defined by an inside facingsurface 54, and an outside facing surface 55. The main body 53 of thesecond end plate 42 also has a peripheral edge 56. Located atpredetermined locations about the peripheral edge 56 are tie rodapertures 57 which extend between the inside and outside facing surfaces54 and 55, respectively. The tie rod apertures 57 are operable toreceive suitable tie rods which will be discussed below.

As seen in FIG. 4, it will be appreciated that this form of the protonexchange membrane fuel cell stack 40 includes multiple tie rodsgenerally indicated by the numeral 60. These multiple tie rods orcouplers, in this form of the invention, include first, second, thirdand fourth tie rods 61, 62, 63 and 64, respectively. The multiple tierods each have a first end 65 which is operable to engage the outsidefacing surface 55 of the second end plate 42, and an opposite, threaded,second end 66 which is operable to be engaged by a suitable nut 67 whichlies in force transmitting engagement relative to the outside facingsurface 45 of the first end plate 41. In the depicted form of theinvention as seen in FIG. 4, it will be appreciated that the tie rods 60are operable to be received through the tie rod apertures 50 and 57 ofthe first and second end plates 41 and 42, respectively. The tie rods 60are also operable to be received through the multiple fuel cell stackmodule frames, which will be described in greater detail hereinafter. Aswill be appreciated, by tightening the nuts 67 relative to each of therespective tie rods 60, the first and second end plates 41 and 42 aredrawn toward each other, and in combination, exert a compressive forceof less than about 60 pounds per square inch to each of the respectivefuel cell stack modules, as will be described in greater detail below.In an alternative form of the invention, and which is not illustrated,but will be appreciated from a study of FIG. 4, the individual tie rodsor couplers 60 individually cooperate with, and connect, the respectivefirst and second end plates 41 and 42 together. However, in this form ofthe invention, the individual first and second end plates 41 and 42 aresomewhat enlarged from the view seen in FIG. 4. In this form of theinvention, the multiple tie rods or couplers 60 do not pass through therespective fuel cell stack modules as will be described with respect tothe form of the invention below, but rather are located exteriorlyrelative to the fuel cell stack modules. In this unillustrated form ofthe invention, the first and second end plates 41 and 42 still exert acompressive force of less than about 60 pounds per square inch to eachof the respective fuel cell stack modules.

Referring now to FIG. 7, another form of the proton exchange membranefuel cell stack is shown, and which is generally indicated by thenumeral 70. In this form of the invention, the proton exchange membranefuel cell stack 70 similarly has a first end plate 71, and a second endplate 72. As seen in that drawing, the first end plate has a main body73 defined by a peripheral edge 74. Still further, the main body has anoutside facing surface 75. As with the earlier form of the inventiondescribed, the main body 73 has a fuel gas passageway 76 and an exhaustgas passageway 77 formed therein. The fuel gas passageway 76 allows asource of a fuel gas 30 to be supplied to the proton exchange membranefuel cell stack 70. The exhaust gas passageway 77 allows exhaust gases,which may include unused fuel gas as well as water vapor, to escape fromthis form of the invention 70. As seen in FIG. 7, the second end plate72 has a main body 80. The main body has an outside facing surface 81,and an opposite inside facing surface 82. Still further, the main body81 is defined by a peripheral edge 83. As illustrated in FIG. 7, a firstreleasable coupler 84 having a first end 85, and an opposite, second end86, is individually affixed to the first and second end plates 71 and72, respectively. A second and opposite coupler 88 may also be providedon the opposite side of the fuel cell stack 70 and is similarly affixedto the first and second end plates 71 and 72. The coupler 84 further hasa moveable latch assembly 87 and which is operable, when fully engagedor closed, to cause the first and second end plates 71 and 72 to beforcibly moved together thereby exerting a compressive force on theindividual fuel cell stack modules, as will be discussed in greaterdetail hereinafter, of less than about 60 pounds per square inch. Asseen in the drawings, the coupler 84, having opposite ends 85 and 86,respectively, cooperates with, and forcibly connects the respectivefirst and second end plates 71 and 72 together and does not pass throughthe respective fuel cell modules, as will be described below. Thisarrangement also facilitates the easy repair and replacement ofindividual fuel cell modules in the event of a malfunction or failure.Of course, this coupling arrangement greatly facilitates the servicingof fuel cell stacks in a manner not possible heretofore.

Referring now to FIG. 3, another form of the present invention is shownand which is generally indicated by the numeral 90. As seen in this formof the invention, the proton exchange membrane fuel cell stack 90 has afirst end plate 91, and an opposite second end plate 92. The first endplate has a main body 93 which is defined by an outside facing surface94, and an opposite inside facing surface 95. Still further, the mainbody 93 is defined by a circumscribing peripheral edge 96. Asillustrated, a fuel gas passageway 100 extends between the inside andoutside facing surfaces 94 and 95 and provides a means by which a sourceof a fuel gas 30 may enter the fuel cell stack 90 through a fuel gasfitting 106. An exhaust gas passageway 101 also extends between theinside and outside facing surfaces 94 and 95 and provides a means bywhich any unused fuel gas and/or water vapor may exit the protonexchange membrane fuel cell stack 90 during operation through an exhaustgas fitting 107. As seen in this form of the invention, a plurality offastener receiving apertures 102 are formed in the inside facing surface95 and peripheral edge 96. These fastener receiving apertures 102 areoperable to engage resilient fasteners which are borne by, and whichextend outwardly relative to the respective proton exchange membranefuel cell stack modules, as will be described below. Still further, andas seen in FIG. 3, the first end plate 91 includes a pair of resilientlatch or fastener members 103 which extend normally outwardly relativeto the inside facing surface 95, and which are mounted along theperipheral edge 96 of the main body 93. These individual fastener orlatch members 103 have a distal end 104 which includes an engagementportion 105 which is operable to releasably engage an adjacent,juxtaposed fuel cell stack module, as will be described below, so as toexert a sufficient compressive force relative thereto in order toachieve the benefits of the present invention.

Referring still to FIG. 3, it will be seen that the second end plate 92has a main body 110 which has an outside facing surface 111, and anopposite, inside facing surface 112. As illustrated in the exploded viewof FIG. 3, the main body 110 is also defined by an outside peripheraledge 113, and an opposite inside peripheral edge 114. The insideperipheral edge 114 defines, at least in part, an internal cavity 115which is operable to receive an electrically conductive heat sink, aswill be discussed in greater detail hereinafter. Still further, as seenin FIG. 3, it should be understood that a plurality of air passageways116 are formed in the main body 110, and extend therebetween the outsideperipheral edge 113 and the inside peripheral edge 114. The plurality ofair passageways 116 allow suitable cooling air to pass therethrough andengage the electrically conductive heat sink, discussed in detailhereinafter, which is received within the internal cavity 115 toaccomplish the features of the invention. On the second end plate 92,and more specifically on the peripheral edge 113 of the inside facingsurface 112 thereof, is mounted a plurality of resilient fasteners 117which extend substantially normally, outwardly, relative thereto. Theplurality of fasteners have a distal end 118 which forms an engagementportion 119 for engaging an adjacent fuel cell stack module, as will bedescribed in greater detail hereinafter. The engagement of the pluralityof resilient fasteners 117 with an adjacent fuel cell stack module, aswill be described hereinafter, creates sufficient compressive force soas to achieve the several benefits of the invention as will be discussedin greater detail below.

Referring now to FIG. 12, yet another alternative form of the protonexchange membrane fuel cell stack is shown, and which is generallyindicated by the numeral 130. As seen therein, this form of the protonexchange membrane fuel cell stack has first and second end plates 131and 132, respectively, and which are operable, as in the previous formsof the invention, to exert a compressive force on the fuel cell stackmodules that will be described hereinafter in order to render the protonexchange membrane fuel cell stack 130 operational. In this form of theinvention, the first end plate 131 has a main body 133 which has anoutside facing surface 134, and an opposite inside facing surface 135.Still further, the main body 133 is defined by a circumscribingperipheral edge 136. As seen in FIG. 12, a plurality of resilientfasteners 140 are made integral with the peripheral edge 136 and whichhave a distal engagement portion 141 which resiliently releasablyengages an adjacent fuel cell stack module, as will be described below,thereby releasably affixing the first end plate 131 in forcibleengagement relative thereto. As further illustrated in FIG. 12, thesecond end plate 132 similarly has a main body 142, defined by anoutside facing surface 143, and an opposite inside facing surface 144.It should be understood that the main body 142 is very similar in itsoverall design to that described with the earlier described form of theinvention described in the paragraphs immediately above. In this form ofthe invention, the main body 142 has an outside peripheral edge 145which similarly has formed therein a plurality of air passageways 146which allow a source of cooling air to pass therethrough and come intoheat removing contact relative to an electrically conductive heat sink,which will be described in detail in the paragraphs which follow. In thepresent form of the invention, and as seen in FIG. 12, it should beappreciated that a fuel gas manifold 150 is provided and which spansbetween the first and second end plates 131 and 132. The fuel gasmanifold 150 is operable to deliver the source of a reactant fuel gas 30to the respective fuel cell modules, through a fuel gas fitting 152, torender them individually operational in the manner, as will be describedin greater detail below. Still further, in this form of the invention130, an exhaust gas manifold 151 is provided and which is coupled influid receiving relation relative to the respective proton exchangemembrane fuel cell stack modules, as will be discussed in greater detailhereinafter, to remove any unused fuel gas and/or water vapor through anexhaust gas fitting 153. In this form of the invention, as in theprevious forms of the invention, it should be understood that the firstand second end plates 131 and 132 are releasably fastened to theadjacent fuel cell stack modules which are positioned therebetween. Thisfastening arrangement generates a compressive force which is applied tothe respective fuel cell stack modules, as described hereinafter, inorder to render the PEM fuel cell stack 130 fully operational.

Referring now to FIG. 21, yet another, alternative form of the protonexchange membrane fuel cell stack is shown, and which is generallyindicated by the numeral 160 therein. As seen in this form of theinvention, the present invention includes first and second end plates161 and 162 which operate in a manner similar to the end platesdescribed in the previous forms of the invention discussed, above. Inthis regard, the first end plate 161 is defined by a main body 163having an outside facing surface 164 and an opposite inside facingsurface 165. The main body is also defined by an outside facingperipheral edge 166. As illustrated, a fuel gas passageway 170 andexhaust gas passageway 171 are formed in the main body 163, and extendtherebetween the outside and inside facing surfaces 164 and 165,respectively. As earlier discussed, the fuel gas passageway is operableto deliver a source of a reactant fuel gas 30 to the fuel cell stackmodules, as will be described below, in order to render the PEM fuelcell stack 160 operational. Similarly, the exhaust gas passageway 171 isoperable to remove unused fuel gas and water vapor which may be producedas a byproduct of the operation of the PEM fuel cell stack 160, as willbe described in greater detail in the operation phase of thisapplication. Similar in some respects to other forms of the inventiondescribed above, a plurality of fastener receiving apertures 172 areformed in the inside facing surface 165, and peripheral edge 166 of themain body 163, and are operable to receive resilient fasteners whichextend normally outwardly relative to the individual fuel cell stackmodules that will be described below. As seen in FIG. 21, the second endplate 162 is also defined by a main body 173, and which has an outsidefacing surface and an opposite inside facing surface 175. As should beunderstood, the inside facing surface defines, at least in part, acavity for receiving an electrically conductive heat sink (not shown).Still further, the main body has an outside facing peripheral edge 176which has a plurality of air passageways 177 formed therein. The airpassageways 177 allow a source of cooling air to reach, and come intoheat removing relation relative to, an electrically conductive heat sinkwhich is contained within the cavity which is defined, at least in part,by the inside facing surface 175. This is similar to the earlier form ofthe invention as seen in FIG. 3. Again this form of the invention 160operates in a manner similar to the earlier forms of the inventiondiscussed, above, whereby the individual first and second end plates 161and 162 are fastened to adjacent fuel cell modules, as will be describedbelow, in a fashion whereby a compressive force is generated in a mannerwhich allows the proton exchange membrane fuel cell stack 160 to berendered fully operational.

Referring now to FIG. 2 and following, it will be understood that aproton exchange membrane fuel cell stack in the various forms 40, 70,90, 130, 160, as already identified, and which may be incorporated in aPEM fuel cell stack power system 10, includes a plurality of repeating,serially electrically coupled fuel cell stack modules which aregenerally indicated by the numeral 180. The plurality of fuel cell stackmodules 180 are disposed between the first and second endplates 41 and42; 71 and 72; 91 and 92; 131 and 132; and 161 and 162, discussedheretofore, and are sealably mounted together by a compressive force ofless than about 60 pounds per square inch. This compressive force may beapplied by means of the various end plates 41 and 42; 71 and 72; 91 and92; 131 and 132; and 161 and 162, as well as coupler assemblies, such asthe multiple tie rods 60 and the releasable coupler 84. Still further,other fastening arrangements as will be described below will alsogenerate the compressive force. It should be understood that each of thefuel cell stack modules 180 comprise a frame. In this regard, theinvention contemplates at least five different proton exchange membranestack module frames, which will be referred to hereinafter as merely a“frame.” In this regard, the respective frames include a first form 181,as best seen in FIG. 3; a second form 182, as best seen in FIGS. 5 and9; a third form 183, as best seen in FIG. 8; a fourth form 184, as bestseen in FIG. 10; and a fifth form 185, as best seen in FIG. 21. In theparagraphs which follow, it should be understood that like numbers referto like structures in the individual frame forms 181-185, respectively.It will be appreciated from the discussion which follows that therespective frame forms have subtle variations which provide advantagesto the various forms of the invention as described. These features willbe discussed in greater detail in the paragraphs which follow. In thisform of the invention, each of the respective frames are fabricated froma thermoplastic injection moldable plastic, although other materials maybe suitable.

The respective proton exchange membrane fuel cell stack frames, in theirvarious forms 181-185, respectively, are shown in FIGS. 8-10. Withrespect to the various forms of the frames 181-185 respectively, it willbe appreciated that the respective frames 181-185 each have a main body200. The main body 200 is defined by a first side 201, and an oppositesecond side 202. The first and second sides are disposed inpredetermined spaced relation by an outside peripheral edge 203 whichhas a given width dimension. Still further, the main body 200 has aninside peripheral edge 204 which defines an internal cavity 205. As bestseen by reference to FIG. 2, and following, it will be appreciated thatan air passageway 206 is formed in the peripheral edge 203, and extendsbetween the inside and outside peripheral edges 203 and 204,respectively. This air passageway 206 communicates with the internalcavity 205 thereof. It should be understood from studying the variousforms of the frames 181-185, that the frames are substantiallyself-aligning as will be described in greater detail hereinafter. Thisfeature of the invention greatly facilitates the effective assembly ofthe same invention.

The various forms of the frame 181-185, respectively, each have amounting flange 210 which is made integral with the inside peripheraledge 204 of the main body 200, and which extends into the internalcavity of the frame 205. The mounting flange 210 has a first side 211which is disposed in a substantially coplanar orientation relative tothe first side of the frame 201, and a second side 212. A thicknessdimension 213 (FIG. 5) is defined between the first side 211 and thesecond side 212 of the mounting flange 210. Still further, the mountingflange defines an inside peripheral edge 214 (FIG. 3) which defines anaperture 215 which communicates with the internal cavity 205 of theframe 180. Each of the several forms of the frames 181-185,respectively, have formed therein a fuel gas passageway 220 whichextends through the respective main body 200 of the frame 180 andcommunicates with the internal cavity of the frame 205. In this regard,the respective fuel gas passageways 220 have a first end 221 (FIG. 5)which is coupled in fluid flowing communication relative to the fuel gaspassageway 51, 76, 100, 170, as defined by the end plates 41, 42, 71,72, 91, 92, 131, 132, 161, 162, of the various forms of the invention40, 70, 90, and 160, described earlier. Therefore, a source of areactant fuel gas 30 provided to the fuel gas passageways as defined byan end plate of the various forms of the invention would thereby passthrough the end plates and travel along the substantially coaxiallyaligned fuel gas passageway 220 formed in the frames 180, and bereceived within the internal cavity of the frame 205. As should beunderstood, and in one form of the invention, the second end 222 of thefuel gas passageway 220 of a respective frame 181-185 is positioned influid flowing relation relative to the first end 221 of a fuel gaspassageway 220 of an adjacent frame. Still further, and as best seen inthe drawings, a plurality of fuel gas channels 223 (FIG. 5) are formedin the first side 201 of the main body 200, and which couple the fuelgas passageway 220 in fluid flowing relation relative to the internalcavity 205 of the frame 181-185 and to the aperture 215 which is definedby the inside peripheral edge 214 of the mounting flange 210. Stillfurther, it will be recognized by a study of the drawings such as FIG.5, that the first side 201 of the main body 200 further has formedtherein an exhaust gas passageway 224 which has a first end 225 and anopposite second end 226. Similar to that discussed above, the first end225 of the exhaust gas passageway 224 is coupled in fluid flowingrelation relative to the exhaust gas passageway 52, 77, 101, 171, asdefined in the respective end plates 41, 71, 91, 131, 161, as earlierdisclosed. Similarly, the second end 226 is coupled in fluid flowingrelation relative to the first end 225 of an adjacent main body 200. Itwill be seen in FIG. 5 that a plurality of exhaust gas channels 227 areformed in the first side 201 of the main body 200 thereby coupling theinternal cavity 205 and the aperture 215 in fluid flowing relationrelative to the exhaust gas passageway 224. As will be appreciated, thefuel gas 220 and exhaust gas passageways 224 of the respective fuel cellstack modules 180 are coupled in fluid flowing relation one relative tothe other in one possible form of the invention.

Referring now to FIG. 12, it should be understood that in the form 130of the invention as seen therein, a fuel gas passageway 230 mayalternatively be formed in the outside peripheral edge 203 of a frame180 so as to be coupled in fluid flowing relation relative to a fuel gasmanifold 150. Similarly, an exhaust gas passageway (not shown) may bealternatively formed in the outside peripheral edge 203 of a frame 180so as to be coupled in fluid flowing relation relative to an exhaust gasmanifold 151. Referring now to FIG. 10, and in another alternative formof the invention, an exhaust gas passageway 231 may be formed in theoutside peripheral edge 203 of the frame 180 in a manner such that theexhaust gasses formed by the proton exchange membrane fuel cell stack,and which may include unused fuel gas and water vapor formed as abyproduct of the operation of the fuel cell stack, may be vented to theambient environment. In one possible form of the invention 40 as seen inFIG. 4, one of the frames 180 which is positioned adjacent to the firstend plate 41 does not include the aperture 215. Rather, the first side201 of the frame 180 is substantially continuous and is forcibly engagedby the adjacent end plate. This is similarly the case for the form ofthe invention 90 as seen in FIG. 3, and wherein the second end plate 92,and which appears quite similar to the frames 180 that are positionedtherebetween. The first and second end plates 91 and 92 has asubstantially continuous outside facing surface 94 and does not definean aperture 215 which communicates with the internal cavity 115 thereof.

As best seen by reference to FIGS. 9 and 11, for example, and in oneform of the invention, the various forms of the frames 181-185 mayinclude a plurality of alignment cavities 240 (FIG. 11) which are formedin predetermined positions in the first side 201 of the frame 180 andwhich are operable to matingly receive or nest a plurality of malealignment members 241 which are borne on, and otherwise extend outwardlyrelative to, the second side 202 of an adjacent frame 180 which isjuxtaposed relative thereto. As should be understood, a passageway may,but does need to, extend through and between 241 and 242 (not shown).The first male alignment member 241 is operable to be received ormatingly nested within the individual alignment cavities 240 in thenature of a friction-fit. This telescoping receipt of the male alignmentmember within the individual alignment cavities 240 facilitates theself-alignment of the respective frames 181-185 one relative to theother. This greatly facilitates the accurate and rapid assembly of theindividual proton exchange membrane fuel cell stacks 40, 70, 90, 130 and160, as described herein. It will be recognized that O-ring seals 244,are employed in order to seal the respective fuel gas passageways 220and exhaust gas passageways 224 of adjacent fuel cell stack modulestogether. In some forms of the invention, as seen in FIG. 4, forexample, the plurality of tie rods or couplers 61-64, respectively, arereceived through the individually coaxially aligned alignment cavitiesand male alignment members so as to allow the end plates 41 and 42 ofthe specific form of the proton exchange membrane fuel cell stack 40 tobe forcibly joined or coupled together. In an alternative form of theinvention 90 as seen in FIG. 3, the earlier mentioned alignment cavities240 and male alignment members 241 are eliminated in favor of aplurality of resilient fasteners 242 which are mounted on, and extendnormally outwardly relative to, the second side 202 of the main body200. The plurality of resilient fasteners 242 are individually coaxiallyaligned so as to be received within a plurality of fastener receivingapertures 243 which are formed in the first side 201 of the main body200 of an adjacent frame 181-185 in the nature of a snap-fit. Theindividual resilient fasteners 242 may be accessed so as to release anadjacent fuel cell module by means of a plurality of fastener receivingapertures 243 which extend, in part, through the outside peripheral edge203 as seen in FIG. 3. When this form of the invention is utilized, theindividual frames 181-185 may be assembled in a fashion whereby anappropriate amount of force is exerted by the individual frames 180, onerelative to another, so as to achieve the benefits of the presentinvention, and without the use of couplers such as described with someforms of the invention. Therefore, the plurality of resilient fasteners242 and fastener receiving apertures 243 in combination provide the sameself-alignment features for the respective frames 180 when they areoriented in an operational relationship one relative to the other, andare further operable to engage a fastener receiving apertures 243 of anadjacent frame so as to provide an appropriate mating relationship so asto achieve the benefits of the present invention.

Referring now to FIG. 21, it will be understood by comparing that viewwith that of FIG. 3, that in this form 185 of the frame 180 that thenumber and cross-sectional areas of the respective air passageways 206,as defined by the main body 200 may be varied so as to achieve anoperationally effective heat dissipation from the proton exchangemembrane fuel cell stack 160 during operation. In the present form ofthe invention 160 as seen in FIG. 21, as well as the other forms of theinvention as seen in the drawings, it should be understood that theproton exchange membrane fuel cell stack 160 has an operationallyeffective temperature when the most optimal amount of electrical poweris generated by the PEM fuel cell stack 160 during operation. In thepresent invention as disclosed, the individual proton exchange membranefuel cell modules 180 are each maintained at an operational temperaturewhich is within less than about 10% relative to any other fuel cellmodules 180 as contained within the same proton exchange membrane fuelcell stack 40, 70, 90, 130 and 160.

Referring now to FIG. 3 and following, each of the proton exchangemembrane modules 180, as disclosed herein, includes a sealing member 250which is sealably affixed to the first side 201 of each of the mainbodies 200 of the frames 181-185, and which is positioned adjacent tothe outside peripheral edge 203 thereof. Positioned in substantiallysealing relation and in alignment relative to the individual frames181-185, respectively, is a current collecting separator plate generallyindicated by the numeral 251. The current collecting separator plate 251is generally a non-porous, substantially smooth plate normallyfabricated from an electrically conductive metal. The current collectingseparator plate 251, which matingly cooperates with and is substantiallyself-aligning relative to the respective frames 181-185, has a firstinside facing surface 252, and an opposite second, outside facingsurface 253. When appropriately positioned relative to the first side201 of the main body 200, the inside facing surface 252 is disposed incovering relation relative to and substantially seals the respective(and exemplary) fuel gas channels 223 and exhaust gas channels 227 (FIG.11), respectively, thereby confining the reactant or fuel gas 30, andany unused reactant gas and/or water vapor to those channel regions 223,221. As seen in the drawings, the current collecting separator plate 251is defined by a peripheral edge 254 and in some forms of the invention,the current collecting separator plate has an electrically conductivetab 255 which extends outwardly relative to the outside peripheral edge203 of the main body 200 of each of the frames 181-185 for purposes ofallowing the removal of electricity, or further allowing an electricalsignal to be transmitted from same. This would, for example, allow theinvention to be monitored by a digital control system 15 as seen inFIG. 1. In other forms of the invention, electrically conductive tabs255 on one more current collecting separator plates 251 may be used toelectrically segment the fuel cell stack 40, 70, 90, 130 160 as taughtin U.S. Pat. No. 6,703,155, which is incorporated by reference herein.In one form of the invention as seen in FIG. 5, a plurality of alignmentapertures 256 may be formed along the peripheral edge 252 so as toaccommodate either male alignment members 241; or a plurality ofresilient fasteners 242 of an adjacent frame 181-185 to passtherethrough. In some forms of the invention, the same currentcollecting separator plate 251 will have both a fuel gas passageway 257,as well as an exhaust gas passageway 258 formed therein, and which willbe substantially coaxially aligned relative to the fuel and exhaust gaspassageway 220 and 224 formed in the adjacent main body 200.

Each of the proton exchange membrane fuel cell modules 180 include andenclose, in an appropriate orientation, a first porous gas diffusionlayer which is generally indicated by the numeral 270. In one possibleform of the invention, the first gas diffusion layer comprises, at leastin part, a porous electrically conductive ceramic material layer whichis selected from the group consisting essentially of titanium diboride,zirconium diboride, molybdenum disilicide, titanium disilicide, titaniumnitride, zirconium nitride, vanadium carbide, tungsten carbide, andcomposites, laminates, and solid solutions thereof. The porouselectrically conductive ceramic material which is typically selected hasan electrical resistivity of less than about 60 micro-ohm-centimeters,has a permeability that lies in a range of greater than about 5Gurley-seconds to less than about 2000 Gurley-seconds, and further has apore size of about 0.5 to about 200 microns. Additionally, the firstporous gas diffusion layer 270 has a main body 271 which has an outsidefacing surface 272 which is positioned in a substantially coplanarorientation relative to the first side 201 of the main body 200, and asecond, inside facing surface 273. As should be understood, the mainbody 271 has a thickness dimension approximately equal to the thicknessdimension 213 as defined between the first and second sides 211 and 212of the mounting flange 210. Still further, the main body 271 is sized soas to substantially occlude the aperture 215 which is defined by theinside peripheral edge 214 of the mounting flange 210. It is recognizedthat the fuel gas channels 223 formed on the first side 201 of the frame181-185, as discussed above, deliver a source of fuel gas 30 to thefirst gas diffusion layer 270. The outside facing surface 272 of thefirst porous electrically conductive gas diffusion layer 270 is placedinto ohmic electrical contact thereagainst the inside facing surface 252of the current collecting separator plate 251, which is sealably mountedon the first side 201.

Referring now to FIG. 6, the present invention includes a circumscribinganode seal 280, which is received within the internal cavity of theframe 205, and which is fitted therealong, and rests in sealable contactthereagainst the second side 212 of the mounting flange 210. The anodeseal 280 may be formed from a pressure sensitive adhesive, or othermeans of sealing and bonding, the shape of which will generally followthat of the second side 212 of the mounting flange 210.

As shown in FIGS. 3-6, the present invention also includes a PEMmembrane electrode assembly (MEA) which is generally indicated by thenumeral 310. The PEM MEA is well known in the art and further discussionregarding its composition and operation is not warranted other than tonote that PEM fuel cells normally have an operational temperature whichis less than about 200 degrees C. Further, one skilled in the art willreadily recognize that the PEM MEA generates water as a byproduct duringoperation. It has long been known that some amount of water must bepresent to render the MEA fully operational. Further, if too much wateris present, the MEA will not operate optimally. As shown in FIG. 23, theMEA comprises a proton exchange membrane 290 which has a first anodeside 291, and has an opposite, second cathode side 292. Still further,the MEA is defined by an active area which is generally indicated by thenumeral 293. An anode electrode catalyst layer 295 is applied to theactive area 293 of the anode side 291 of the membrane 290. A cathodeelectrode catalyst layer 296 is applied to the active area 293 of thecathode side 292 of the membrane 290. The possible compositions of theseelectrode catalyst layers 295 and 296 are well known in the art, and therelative compositions of the anode and cathode electrode catalyst layersmay differ. Also, as shown in FIGS. 3-7, the MEA also includes aperipheral edge 294 which is outside of the active area 293 and whichsealably rests thereagainst the anode seal 280 and thereby sealablysecures the MEA or the proton exchange membrane to the mounting flange210. The compressive force of less than about 60 pounds per square inchthat is applied to each of the fuel cell stack modules 180, as disclosedabove, applies a proton exchange membrane sealing force to the mountingflange 210, against the anode seal 280, which lies in a range of about 5to about 50 pounds per square inch.

In some forms of the invention, the first porous electrically conductivegas diffusion layer 270 may be a porous carbon layer or plate. Stillfurther, in another possible form of the invention as seen in FIGS. 25and 26, the first porous electrically conductive gas diffusion layer 270may further include a porous metalized layer 275 which is applied to thesecond outside facing surface 272. Such a layer is disclosed in U.S.Pat. No. 6,716,549, the teachings of which are incorporated by referenceherein. In this regard, this porous metal coating or layer 275 isselected from the group of metals consisting essentially of aluminum,titanium, nickel, iron, stainless steel, manganese, zinc, chromium,copper, zirconium, silver, and tungsten, and their alloys, nitrides,oxides, and carbides. In the form of the invention shown in FIG. 25, thefirst gas diffusion layer 270 with the metal coating 275 is juxtaposedrelative to the anode side 311 of the MEA 310. The metal coating 275allows the porous gas diffusion layer 270 to make an effective ohmicelectrical contact therewith the current collecting separator plate 251.

In one possible form of the invention as seen in FIG. 22, the firstporous electrically conductive gas diffusion layer 270 may include anelectrode or catalyst layer 274 which is bonded or applied to a surfacethereof, here illustrated as the first inside facing surface 273. Inthis case, the anode side 291 of a proton exchange membrane 290 is thenjuxtaposed relative to the catalyst layer 274, which is bonded orapplied to the first conductive gas diffusion layer 270. Likewise, inthe form of the invention as seen in FIG. 26, a catalyst layer 274 isapplied to one surface of the porous gas diffusion layer 270 upon whicha porous metal coating 275 is applied to the opposite surface therefore.The anode side 291 of a proton exchange membrane 290 is then juxtaposedrelative to the catalyst layer 274.

Referring now to FIG. 3 and following, it will be understood that therespective fuel cell stack modules 180 further include a second gasdiffusion layer which is generally indicated by the numeral 300, andwhich is positioned within the internal cavity 205 of the respectiveframes 181-185, and which is juxtaposed relative to the cathode side 312of the proton exchange membrane 310. The second gas diffusion layer 300is typically fabricated from an electrically conductive ceramic materialwhich may be similar to that formed of the first porous gas diffusionlayer 270, although the compositions of the first and second gasdiffusion layers 270 and 300 may differ. The second gas diffusion layer300 has a main body 301 which has a first inside facing surface 302,which lies in juxtaposed relation relative to the cathode side 312 ofthe MEA 310; and an opposite, second or outside facing surface 303.Still further, the main body is defined by a peripheral edge 304. Asseen in FIGS. 22 and 26, in some forms of the invention, a catalystlayer 305 may be first applied to the inside facing surface 302.Thereafter, the proton exchange membrane 290 may be bonded therebetweenthe first gas diffusion layer 270 and the second gas diffusion layer300. In the form of the invention as seen in FIG. 23, the protonexchange membrane 290 has catalyst layer 295 applied to the oppositeanode and cathode sides thereof 291 and 292, and thereafter the firstand second porous gas diffusion layers 270 and 300 may be bonded tosame. FIG. 24 shows another form of the invention and wherein the secondporous gas diffusion layer 300 has a larger size than that of the firstporous electrically conductive ceramic gas diffusion layer 270. In thiscase, the size of the second gas diffusion layer 300 is such that iffully occludes the internal cavity 205 of the frame 181-185, whereas thefirst gas diffusion layer 270 is sized to fully occlude the smalleraperture 215 defined by the inner peripheral edge 214 of the MEAmounting flange 210.

In still another possible form of the invention as best seen in FIGS. 25and 26, the porous electrically conductive ceramic gas diffusion layers270 and 300, respectively are coated with individual catalyst layers305, and a porous metal coating 275 and 306, respectively. The metalcoating 306 is similar to that earlier disclosed with respect to thecoating or metalized layer 275 which is applied to the first ceramicelectrically conductive layer 270. When assembled, the proton exchangemembrane 290 in combination with the catalyst layers which arepositioned adjacent thereto comprises a membrane electrode assembly 310which is then received within the internal cavity 205 of the respectiveframes 200. When fully assembled, the first and second gas diffusionlayers 270 and 300, respectively, lie in ohmic electrical contactthereagainst the opposite anode and cathode sides 291 and 292,respectively of the proton exchange membrane 290.

As noted earlier during operation of a PEM fuel cell, water is producedas a byproduct. In previous prior art devices, various schemes andarrangements have been devised so as to effectively manage the waterwhich is produced by the proton exchange membrane so as to provideoptimal electrical output from any resulting fuel cell. One arrangementwhich has been employed heretofore was to provide various coatings ofmaterial to the gas diffusion layer positioned on the anode or cathodeside of an MEA so as to give the gas diffusion layer a greater or lesserdegree of hydrophobicity. By doing so, designers have attempted toretain a sufficient amount of water in the proton exchange membrane soas to maximize the operation of the fuel cell. Regardless of the schemesand methodology employed heretofore, gas diffusion layers have beendesigned so as to retain just enough water to maintain the membrane inan optimally hydrated state, and while simultaneously removing excessivewater from the membrane so as to prevent the membrane from flooding withwater and shutting down the electricity production of the fuel cell.

In the arrangement as discussed in the present application, it should beunderstood that the porous electrically conductive ceramic gas diffusionlayers 270 and 300 are fabricated from porous ceramic materials whichare generally characterized as hydrophilic materials, that is they havean affinity for adsorbing, absorbing, or passing water. In view of thehydrophilic nature of these materials, it was expected that watermanagement issues would result from the use of porous electricallyconductive ceramic material. Through a mechanism which is not completelyunderstood, it was surprisingly discovered that these same porous,ceramic materials employed in, for example, the first and second gasdiffusion layers 270 and 300, somehow retain enough water so as tomaintain the proton exchange membrane 290 optimally hydrated whilesimultaneously allowing gas to pass therethrough. The retention of someamount of water by the porous electrically conductive ceramic gasdiffusion layers 270 and 300 to render a fuel cell operational is quitenovel and unexpected in view of the manner in which ceramic materialshave been utilized heretofore in solid oxide fuel cells (SOFC).Moreover, initial testing of the present invention with ceramic anodeand cathode gas diffusion layers has shown an unexpected increase in theoperating temperature range. While an identical PEM membrane with carbongas diffusion layers would have a maximum operating temperature ofapproximately 46° C., the same membrane with ceramic gas diffusionlayers can operate up to 54° C. without thermal runaway caused bydehydration of the proton exchange membrane. This unexpected featureallows a fuel cell system 10 to operate at higher ambient temperatureconditions. As noted in the background of the invention, SOFC deviceshave employed porous electrically conductive ceramic materials tofabricate the anode and cathode of same. However, in the operation ofSOFC devices, water cannot, nor need not be retained by the ceramic gasdiffusion layers employed with same in view of the high operatingtemperatures) (600-900°). Additionally, and while some amount of wateris necessary to render a proton exchange membrane 290 operational, nowater is necessary to render the ceramic electrolyte used in a SOFCoperational, rather the high temperature of operation of a SOFC rendersthe electrolyte ionically conductive.

Referring now to FIG. 27, in one possible form of the invention, analternative electrically conductive gas diffusion layer 320 is providedand which may be substituted for the first and second electricallyconductive ceramic gas diffusion layers 270 and 300, respectively, asearlier described. In this form of the invention, the electricallyconductive gas diffusion layer 320 may comprise a plurality of sinteredwire meshes of decreasing porosity which are integrally joined togetherin order to provide the advantages that are supplied by means of theelectrically conductive and porous ceramic material which is typicallyutilized in the fabrication of the first and second gas diffusion layers270 and 300, respectively. As seen in that view, the plurality of wiremeshes 321 have decreasing porosity and are sintered in a conventionalmeans thereby becoming a unitary object which may be used in combinationwith a proton exchange membrane 290 as earlier described. In anotherpossible form of the invention, the electrically conductive gasdiffusion layer 320 may be coated with a catalyst layer, and thereaftercombined with a proton exchange membrane 290 as seen earlier withrespect to FIGS. 25-26.

Referring now to FIGS. 22-27, the bonded or juxtaposed combination ofproton exchange membrane 290; electrode or catalyst layers 274, 295,296, or 305; and gas diffusion layer 270 or 300 is often referred to asa membrane electrode diffusion assembly (MEDA) 313. It can now beunderstood by one skilled in the art that in each of the various formsof the invention, at least one of the first or second gas diffusionlayers 270 and/or 300 comprises a material or composition wherein anelectrical conductivity is established between either the first orsecond gas diffusion layer 270 and/or 300 and a component of the fuelcell stack module 180 which is immediately adjacent to the gas diffusionlayer 270 and/or 300 such that the electrical conductivity issubstantially independent of the compressive force applied to each ofthe respective fuel cell stack modules 180. This feature of theinvention allows a compressive force to be applied which issubstantially less than the force normally applied to prior art devices.Stated somewhat differently, the compressive force applied by therespective fuel cell stack module 180 or by the opposite end plates isemployed for purposes of sealing the respective components together;maintaining thermal contact between components; and/or providingrigidity to the product, and is not principally employed to maintain anoperationally effective electrical conductivity. Additionally, it willbe noted that the reduced compressive forces applied to the gasdiffusion layers 270 and 300 improves the respective gas diffusionlayers mass transport capabilities inasmuch as high compressive forceswhich are typically applied in prior art stack arrangements tend tocrush porous materials thereby impeding mass transport therethrough.

Therefore, in one form of the invention, a proton exchange membrane fuelcell stack module 180 is provided and which includes a membraneelectrode assembly 310 having a first, anode side 311, and a secondcathode side 312, and wherein the anode and cathode sides 311 and 312each have an active area surface 293. In this form of the invention, asseen in FIG. 5 for example, the active area of surface 293 of at leastone of the anode and cathode sides 311 and 312 of the MEA 290; and/or afuel cell component such as the first and second gas diffusion layers270 and 300 and/or the current collecting separator plate 251 eachhaving a region which is oriented at least partial covering relationrelative to the active area surface 293 is substantially devoid ofpredetermined passageways for accommodating the flow of a reactant gas.This feature of the invention is quite unique in view of the earlierteachings of many prior art references provided heretofore. Inparticular, it should be noted that the active area surface of eitherthe anode side 291 or cathode side 292 or the associated ceramic gasdiffusion layers 270, 300 is substantially devoid of predetermined gaspassageways for accommodating the flow of a reactant gas. Similarly theadjacent current conducting separator plates is devoid of predeterminedgas passageways extending along its inside or outside facing surfaces.

As best seen by references to FIG. 3 and following, the presentinvention further includes an electrically conductive heat sink 330having a thermally conductive mass and which is received within theinternal cavity of the frame 205, and juxtaposed in ohmic electricalcontact relative to the second gas diffusion layer 300. As seen in thedrawings, the heat sink 330 is oriented in fluid flowing relationrelative to the air passageways 206 which are defined by the frame. Inthe arrangements as seen in the drawings, it will be seen that the heatsink 330 may take on various forms. For example, as seen in FIGS. 13,14, and 15, the heat sink 330 may comprise a reticulated electricallyconductive metal foam 331. An air-cooled fuel cell with a reticulatedmetal foam heat sink is disclosed in U.S. Pat. No. 6,939,636, theteachings of which are incorporated by reference herein. Still further,as seen in FIGS. 16 and 19, the heat sink 330 may comprise a corrugatedor pleated metal heat sink 332 of various forms. In one possible form ofthe invention, the corrugated heat sink could be fabricated of a solidmaterial as shown, or in the alternative, could be fabricated from ametal mesh. Further, and referring now to FIG. 17, the heat sink 330 ofthe present invention may comprise an extruded aluminum plate 333.Moreover, as seen in FIG. 18, the heat sink 330 may comprise a stamped,resilient, reticulated metal heat sink 334. Still further, the heat sink330 may comprise one or more of these same forms 331-334 of the heatsink in combination. Each of the heat sinks 330, described above,includes a main body 340 which has an inwardly facing surface 341 whichis juxtaposed relative to, and positioned in ohmic electrical contactthereagainst, the second electrically conductive ceramic gas diffusionlayer 300. Still further, the respective heat sinks 331-334 has a secondoutwardly facing surface 342 which is positioned in a substantiallycoplanar orientation relative to the second side 202 of the respectiveframes 181-185, respectively. The second outwardly facing surface 342 isplaced in ohmic electrical contact with the current collecting separatorplate 251 of the adjacent fuel cell stack module 180, thus electricallycoupling each of the fuel cell stack modules 180 within the fuel cellstack 40, 70, 90, 130, and 160. It should be understood that if two ormore heat sink forms 331-334 are used in combination, then the outermostheat sink would still have an outwardly facing surface which issubstantially coplanar with the outwardly facing surface 202 of therespective frames 181-185, respectively. Therefore, the respective heatsinks are enclosed within the internal cavity 205 of the respectiveframes 181-185. The respective heat sinks 330 further have a peripheraledge 343 and a thickness dimension which is measured between theinwardly and outwardly facing surfaces 341 and 342, respectively. In oneform of the invention as seen in FIG. 14, the thickness dimension of theheat sink 33 is greater than about 10 millimeters to less than about 100millimeters. Still further, the main body of each of the heat sinks 340has a first end 344 and a second end 345. Each of the main bodies 340 ofthe respective heat sinks 330 define a plurality of air passageways 346which allow the passage of cooling air therethrough in order tofacilitate the removal of heat energy and moisture which is generated bythe proton exchange membrane fuel cell stack 40, 70, 90, 130 and 160during operation. As will be appreciated from the drawings, theplurality of air passageways 346 are oriented in fluid flowing relationrelative to the air passageways 206 which are defined by the respectiveframes 181-185, respectively. As should be understood from a study ofFIGS. 14 and 15, the thermal mass and/or the thickness of the heat sink330 may be varied in order to achieve a substantially uniformoperational temperature for each of the fuel cell modules 180.

In the arrangement as seen in the drawings, it should be understood thateach of the fuel cell stack modules 180 have an operating temperaturewhich is within less than about 10% of any other fuel stack modules 180which are located within the same fuel cell stack 40, 70, 90, 130 and160. Further, in the arrangement as shown in the drawings, it should beunderstood that the thermally conductive mass of the individual heatsinks 330 of each of the fuel cell stack modules 180 provides asubstantially different degree of cooling for each of the respectivefuel cell stacks module 180 within the fuel cell stack 40, 70, 90, 130and 160 so that the resulting operating temperature of any one of theplurality of fuel cell stack modules 180 differs from the operatingtemperature of any other of the plurality of fuel cell stack modules 180by less than about 10%. In the arrangements as seen in the drawings, itshould be understood that the individual modules 180 may haveelectrically conductive heat sinks 330 which have variable thermallyconductive masses. More specifically, those modules 180 which arelocated increasingly inwardly towards the center portion of a protonexchange membrane fuel cell stack 40, 70, 90, 130 and 160 typically willhave thermally conductive masses greater than those fuel cell stackmodules 180 that are positioned closer to the end plates 41 and 42, forexample. This variation in the thermally conductive mass of therespective fuel cell stack modules 180 facilitates the effectivedissipation of heat energy which is a byproduct of the operation of theproton exchange membrane fuel cell stack. Moreover, another possibleform of the invention as best seen in FIGS. 19 and 20, a corrugated orpleated metal heat sink 332, maybe provided with or without variationsin cross-sectional dimensions of the air passageways along the length ofthe heat sink. The pleated metal heat sink 332 is formed from anelectrically conductive substrate which defines a plurality ofpassageways 346 which have various cross-sectional dimensions when thesepassageways are measured between the first and second ends 344 and 345thereof. As seen in the form of the heat sink shown in FIG. 20, it willbe noted that the plurality of air passageways 346 which originate atthe first end 344 have, generally speaking, a wider cross-sectionaldimension than the same air passageways 346 which are located at theopposite second end 345. This variation in the cross-sectionaldimensions of the plurality of passageways provides at least first andsecond air cooling velocities 351 and 352 relative to the respectivepassageways 346. It should be understood that these first and secondcooling air velocities each provide substantially different degrees ofcooling relative to the heat sink 330 along its length as measuredbetween the first and second ends 344 and 345, respectively. Therefore,the heat sinks 330 of the present invention provide a means not only formaintaining a substantially constant operating temperature of less thanabout 10% between the individual fuel cell stack modules 180 within anyfuel cell stack 40, 70, 90, 130 and 160, but further provides a meansfor substantially cooling each module in a substantially uniform way toprovide optimum operational efficiency for each of the respective fuelcell modules regardless of the location of the fuel cell stack modules180 within a proton exchange membrane fuel cell stack 10.

Furthermore, and referring now to FIG. 21 and as earlier discussed, thesame proton exchange membrane fuel cell stack arrangement 160 furtherprovides that the air passageways 206 as defined by the respectiveframes 181 may have variable cross-sectional areas. Therefore, it shouldbe appreciated that the present invention provides not only a means forvarying the thermally conductive mass of each of the respectiveelectrically conductive heat sinks 330 as well as providing variableamounts of air by means of varying the numbers and cross-sectionaldimensions of the air passageways 206 in order to provide an operativelyeffective and substantially uniform operational temperature for theproton exchange membrane fuel cell stack 40, 70, 90, 130 and 160,respectively.

OPERATION

The operation of the described embodiment of the present invention isbelieved to be readily apparent and is briefly summarized at this point.

In one of its broadest aspects, the present invention relates to aproton exchange membrane fuel cell stack 40, 70, 90, 130 and 160 whichincludes a plurality of repeating, serially electrically coupled fuelcell stack modules 180, which are sealably mounted together by acompressive force of less than about 60 pounds per square inch. In thearrangement as seen in the drawings, the fuel cell stack modules 180each have an operating temperature which is within less than about 10%of any other of the fuel cell stack modules 180 which are located withinthe same proton exchange membrane fuel cell stack. This compressiveforce applies a proton exchange membrane sealing force to the mountingflange 210 which lies in a range of about 5 pounds PSI to about 50pounds PSI. In the arrangement as seen in the various drawings, theproton exchange membrane fuel cell stack 40, 70, 90, 130 and 160 has anoperationally effective conductivity as measured between the first andsecond end plates 41, 42; 71, 72; 91, 92; 131, 132; 161 and 162, andwhich is achieved at a pressure less than the compressive force appliedby the first and second end plates. This is indeed unique relative toprior fuel cell stacks disclosed heretofore and wherein substantialcompressive force was applied by the end plates of these prior artdevices in order to facilitate an appropriate operationally effectiveconductivity and further to achieve appropriate sealing of theindividual proton exchange membrane fuel cell components positionedtherebetween. Additionally, these prior art devices suffer from problemsassociated with undue heat accumulation in various portions of PEM stackand variability in their operationally effective conductivity in view ofinappropriate hydration, and other problems that are well known in theart.

In the arrangement as seen in the drawings, the anode side 291 of theproton exchange membrane 290 has an active area 293. In one possibleform of the invention, the active area 293 of the proton exchangemembrane 290; or the current collecting separator plate 251 which ispositioned in at least partial covering relation relative thereto areboth substantially devoid of predetermined passageways for accommodatingthe flow of a reactant gas 30. This is indeed unique and novel relativeto previous proton exchange membrane fuel cell stacks where ratherelaborate predetermined passageways have been utilized, heretofore, tomanage the flow of reactant gas and to optimize the performance of theseprior art devices.

Another aspect of the present invention relates to a proton exchangemembrane fuel cell stack 40, 70, 90, 130 and 160 which includes firstand second endplates 41, 42; 71, 72; 91, 92; 131, 132; 161 and 162,which are disposed in substantially parallel spaced relation onerelative to the other; and a plurality of repeating, air-cooled, fuelcell stack modules 180 are positioned between the first and secondendplates, and which are serially electrically coupled together, andwherein the respective endplates sealably couple the respective fuelcell stack modules 180 together by applying, at least in part, acompressive force of less than about 60 pounds per square inch to eachof the respective fuel cell stack modules 180, and wherein the protonexchange membrane fuel cell stack has an operational temperature profileas measured between the first and second end plates which varies by lessthan about 10%. As noted earlier, the proton exchange membrane fuel cellstack has an operationally effective conductivity, as measured betweenthe first and second endplates which is achieved at a pressure which isless than the compressive force which is experienced by the respectiveproton exchange modules 180.

Another aspect of the present invention relates to a proton exchangemembrane fuel cell stack module 180 which includes a proton exchangemembrane 290 having an anode side 291, and a cathode side 292; a firstgas diffusion layer 270 juxtaposed relative to the anode side 291; asecond gas diffusion layer 300 juxtaposed relative to the cathode side292; an electrically conductive heat sink 330 having a thermallyconductive mass juxtaposed relative to the second gas diffusion layer300; and a current collecting separator plate 251 juxtaposed in ohmicelectrical contact relative to the first gas diffusion layer 270. In thearrangement as seen in the various drawings, the plurality of fuel cellstack modules 180 are electrically connected in series, and are furthermounted between a first and second endplates 41, 42; 71, 72; 91, 92;131, 132; 161 and 162 to form a fuel cell stack 40, 70, 90, 130 and 160.In the drawings, the current collecting separator plate 251 of a firstfuel cell module 180 is juxtaposed relative to the first endplate, andwherein the heat sink 330 of a remote, second fuel cell module 180 ispositioned in force receiving relation relative to the second endplate.The first and second endplates provide a compressive force of less thanabout 60 pounds per square inch to each of the plurality of protonexchange membrane fuel cell stack modules.

Still another aspect of the present invention relates to a protonexchange membrane fuel cell stack 40, 70, 90, 130 and 160 which includesa plurality of repeating, serially electrically coupled fuel cell stackmodules 180, and which are sealably mounted together by a compressiveforce of less than about 60 pounds per square inch, and wherein therespective fuel cell stack modules 180 further comprise a frame 181-185having an inside and an outside peripheral edge 204, 203, respectively,and first and second sides 201 and 202, respectively. The insideperipheral edge 204 defines an internal cavity 205, and wherein therespective frames 181-185 are self-aligning and matingly nest togetherin an operational orientation. The respective frames 181-185 each definean air passageway 206 which extends between the inside and outsideperipheral edges and which communicates with the internal cavitythereof.

In still another aspect of the present invention a proton exchangemembrane fuel cell stack module 180 is provided and which furtherincludes a proton exchange membrane 290 having an anode side 291, and acathode side 292; and a first gas diffusion layer 270 juxtaposedrelative to the anode side 291. In this arrangement, a second gasdiffusion layer 300 is provided and which is juxtaposed relative to thecathode side 292. Still further, an electrically conductive heat sink330 is juxtaposed relative to the second gas diffusion layer 300. Yetfurther, a frame 181-185 having an inside and an outside peripheral edge204 and 203, respectively, and first and second sides 201 and 202 areprovided. In this arrangement, the inside peripheral edge 204 defines aninternal cavity 205 therewithin the individual frames 181-185,respectively. Still further, the proton exchange membrane 290, the firstand second gas diffusion layers 270 and 300, respectively, and the heatsink 330 are enclosed within the internal cavity 205. Still further, afirst current collecting separator plate 251 is mounted on the firstside 201 of the respective frames 181-185, respectively. The currentcollecting separator plate 251 is juxtaposed relative to the first gasdiffusion layer 270, so as to form a fuel cell stack module 180. In thearrangement as seen in the drawings, a plurality of fuel cell stackmodules 180 are positioned between a first and a second endplate 41, 42;71, 72; 91, 92; 131, 132; 161 and 162, and are further seriallyelectrically coupled together, and wherein the respective endplatesapply a compressive force of less than about 60 pounds per square inchon each of the respective fuel cell stack modules 180. In thearrangement as seen in the various drawings, the first and second gasdiffusion layers 270 and 300, respectively comprise, at least in part, aporous electrically conductive ceramic material layer. This ceramicmaterial layer is selected from the group consisting essentially oftitanium diboride, zirconium diboride, molybdenum disilicide, titaniumdisilicide, titanium nitride, zirconium nitride, vanadium carbide,tungsten carbide, and composites, laminates, and solid solutionsthereof.

Another aspect of the present invention relates to a proton exchangemembrane fuel cell stack 40, 70, 90, 130 and 160, and which includes aplurality of repeating serially electrically coupled fuel cell stackmodules 180, each defining an internal cavity 205, and which are furthersealably mounted together by a compressive force of less than about 60pounds per square inch. Still further, a proton exchange membrane 290 isprovided ad which is placed in an operational orientation relative to atleasfone ceramic gas diffusion layer 270 or 300 and which is furtherreceived within the cavity 205 of the respective fuel cell stack modules180.

In still another aspect of the present invention a proton exchangemembrane fuel cell stack 40, 70, 90, 130 and 160 includes first andsecond endplates 41, 42; 71, 72; 91, 92; 131, 132; 161 and 162, whichare disposed in substantially parallel spaced relation; and a pluralityof repeating, air-cooled, fuel cell stack modules 180 are positionedbetween the first and second endplates, and which are seriallyelectrically coupled together, and which further has an operationallyeffective conductivity, as measured between the first and secondendplates, and which is achieved at a pressure less than a compressiveforce applied to each of the plurality of the fuel cell stack modules180, and which further has an operationally effective temperatureprofile as measured between the first and second end plates which issubstantially uniform.

In still another aspect of the present invention includes a protonexchange membrane fuel cell stack module 180. The module 180 encloses aproton exchange membrane 290 having an anode side 291 and a cathode side292; and a first electrically conductive ceramic layer 270 is juxtaposedrelative to the anode side. In this form of the invention a secondelectrically conductive ceramic layer 300 is provided and which isjuxtaposed relative to the cathode side; and an electrically conductiveheat sink 330 is juxtaposed relative to the second electricallyconductive ceramic layer. In this form of the invention, a frame 181-185is provided and which has an inside and an outside peripheral edge 204and 203, respectively. Still further, the frames 181-185 have first andsecond sides 201 and 202, and wherein the inside peripheral edge 204defines an internal cavity 205. In this form of the invention, therespective frames 181-185 each define an air passageway 206 whichextends between the inside and outside peripheral edges 204 and 203,respectively and which communicates with internal cavity 205 thereof.The proton exchange membrane 290, first and second electricallyconductive ceramic layers 270 and 300, respectively, and theelectrically conductive heat sink 330 are each substantially enclosedwithin the internal cavity 205. Still further, in this form of theinvention, a current collecting separator plate 251 is mounted on thefirst side 201 of the frames 181-185, and which is juxtaposed relativeto the first electrically conductive ceramic layer 270.

In still another aspect of the present invention a proton exchangemembrane fuel cell stack 40, 70, 90, 130 and 160 is provided and whichincludes a plurality of proton exchange membrane 290 each having ananode side 291, and a cathode side 292; and a first porous, electricallyconductive ceramic layer 270 juxtaposed relative to the anode side 291of each of the proton exchange membranes 290. Still further, in thisform of the invention, a second porous, electrically conductive ceramiclayer 300 is juxtaposed relative to the cathode side 292 of each of theproton exchange membranes 290, and wherein the proton exchange membranefuel cell stack has an operational temperature which is less than about200 degrees C.

In still another form of the invention, a proton exchange membrane fuelcell stack module 180 is provided and which includes a proton exchangemembrane 290 having an anode side 291, and a cathode side 292, andwherein the anode and cathode sides 291 and 292 each have an active areasurface 293. In one form of the invention, the active area surface 293of at least one of the anode side, or the cathode side 291 and 292 ofthe proton exchange membrane 290, and/or a fuel cell component such asthe first or second ceramic gas diffusion layers 270 or 300,respectively, and/or the current collecting separator plate 251 have aregion which is oriented at least in partial covering relation relativethereto, and which is substantially devoid of predetermined passagewaysfor accommodating the flow of a reactant gas 30.

In each of the forms of the invention as provided, the proton exchangemembrane fuel cell modules 70 each include an electrically conductiveheat sink 330 having an inside and an outside facing surface 341 and342, respectively, and which is received in the internal cavity 205 ofeach of the frames 181-185, respectively, and wherein the inside facingsurface 341 is juxtaposed relative to the second gas diffusion layer 300and the outside facing surface 342 of the heat sink 330 is oriented in asubstantially coplanar orientation relative to the second side 202 ofeach of the frames 181-185, respectively. Still further, the heat sinkis oriented in fluid flowing relation relative to the air passageway 206which is defined by the respective frames 181-185, respectively. Stillfurther, the heat sink 330 has a thickness dimension which is greaterthan about 10 mm. and a thermally conductive mass which may be variedbetween the individual proton exchange membrane fuel cell stack modules180 so as to provide an operationally uniform temperature as measuredbetween the first and second end plates 41, 42; 71, 72; 91, 92; 131,132; 161 and 162, respectively.

Therefore, it will be seen that a proton exchange membrane fuel cellstack power system 10 is described and which provides assortedadvantages over conventional proton exchange membrane fuel cell stackswhich have been utilized heretofore. The present invention is aircooled, easy to manufacture, and assemble, and achieves an operationallyeffective conductivity at pressures less than the amount of pressurenecessary to seal the individual proton exchange membrane modules 180together, and further provides a convenient means for generatingelectrical power in a cost effective manner and which has not beenpossible, heretofore.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A proton exchange membrane fuel cell stack, comprising: multipleserially arranged proton exchange membrane fuel cell modules; anindividual proton exchange membrane fuel cell module including: a framehaving an inside and an outside peripheral edge, and first and secondsides, and wherein the inside peripheral edge defines an internal cavityrelative to the second side; a current collecting separator platemounted on the first side of the frame; a proton exchange membranehaving an anode side and a cathode side; a first electrically conductiveporous layer juxtaposed relative to the anode side; a secondelectrically conductive porous layer juxtaposed relative to the cathodeside; an electrically conductive heat sink juxtaposed relative to thesecond electrically conductive porous layer; wherein the frame definesan air passageway which extends between the inside and outsideperipheral edges and which communicates with the internal cavitythereof, and wherein the proton exchange membrane, the first and secondelectrically conductive porous layers, and the electrically conductiveheat sink are enclosed within the internal cavity effective that boththe second surface of the frame and the electrically conductive heatsink contact a current collecting separator plate of a frame of anadjacent proton exchange membrane fuel cell module.